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Scenario: I'm thinking about telling my family something over the dinner table. But I'm not sure and my sister says:

Is #2 the best one to use?

1. Think about what they would think if you said this over the dinner table.

2. Think about what they would think if you say this over the dinner table. (What kind of 'would' do I have here? Modal 'would' for likely?)

3. Think about what they will think if you say this over the dinner table.

4. Think about what they will probably think if you say this over the dinner table. (So #4 is expressing their ideas, and #2 is asking for their opinions?)

Thanks.
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How about this example?--

Think about what they might think if you say this [over dinner/at the dinner table].

Or,

Think about what they might say if you say this at the dinner table.

(It doesn't sound quite right to say, 'over the dinner table'; better to say, 'over dinner', or 'at the dinner table'.)
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I wouldn't call it wrong, but it's not the most standard form.

... what they will think if you say ...
... what they would think if you said ...

These are the more standard uses.

CJ
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Comments  
2. Think about what they would think if you say this over the dinner table. ( I hear people use 'would' a lot everywhere. This sentence can't be wrong, can it? 'Would' is not a modal here?)

Thanks.
How does anyone know what somebody else will think, or say?

'Would probably' translates easily into 'might'.
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 CalifJim's reply was promoted to an answer.